fix(miner): treat an absent x-ratelimit-remaining header as unknown, not a 0 budget

packages/loopover-miner/lib/opportunity-fanout.ts

@@ -208,12 +208,20 @@ function repoPath(forge: ForgeConfig, target: Target, suffix: string): string {
 }
 
 function recordRateLimit(summary: RateLimitSummary, response: Response): void {
-  const remaining = Number(response.headers.get("x-ratelimit-remaining"));
-  if (Number.isFinite(remaining)) {
-    summary.rateLimitRemaining =
-      summary.rateLimitRemaining === null
-        ? remaining
-        : Math.min(summary.rateLimitRemaining, remaining);
+  // #9678: Headers.get() returns null for an ABSENT header and Number(null) === 0 (which Number.isFinite
+  // accepts) -- so a forge/proxy that omits x-ratelimit-remaining used to record a budget of 0 and pin the
+  // whole fan-out to serial concurrency. Read the raw value and skip a null/blank header before converting,
+  // matching http-retry.ts's `remaining != null` guard; a genuinely-present "0" (or any finite number) is
+  // still recorded, and a present-but-non-numeric value is still skipped by Number.isFinite.
+  const rawRemaining = response.headers.get("x-ratelimit-remaining");
+  if (rawRemaining !== null && rawRemaining.trim() !== "") {
+    const remaining = Number(rawRemaining);
+    if (Number.isFinite(remaining)) {
+      summary.rateLimitRemaining =
+        summary.rateLimitRemaining === null
+          ? remaining
+          : Math.min(summary.rateLimitRemaining, remaining);
+    }
   }
   const resetSeconds = Number(response.headers.get("x-ratelimit-reset"));
   if (Number.isFinite(resetSeconds) && resetSeconds > 0) {

test/unit/miner-opportunity-fanout.test.ts

@@ -479,6 +479,56 @@ describe("fetchCandidateIssues (#2307)", () => {
     expect(result.rateLimitRemaining).toBe(42);
   });
 
+  it("#9678: an ABSENT x-ratelimit-remaining header records no budget (null), not 0", async () => {
+    // A forge/proxy that omits the header: headers.get() is null and Number(null) is 0 (finite) -- before
+    // #9678 this pinned rateLimitRemaining to 0 and serialized the whole fan-out against a budget never reported.
+    const bareContent = () =>
+      Response.json({ type: "file", encoding: "base64", content: Buffer.from("Contributions welcome.", "utf8").toString("base64") });
+    vi.stubGlobal("fetch", async (input: RequestInfo | URL) => {
+      const url = String(input);
+      if (url.endsWith("/contents/AI-USAGE.md")) return Response.json({}, { status: 404 });
+      if (url.endsWith("/contents/CONTRIBUTING.md")) return bareContent();
+      if (url.includes("/issues?")) return Response.json([issue(3)]);
+      return Response.json({}, { status: 404 });
+    });
+
+    const result = await fetchCandidateIssuesWithSummary([{ owner: "acme", repo: "widgets" }], "token", { apiBaseUrl: API });
+
+    expect(result.rateLimitRemaining).toBeNull();
+  });
+
+  it("#9678: a blank/whitespace-only x-ratelimit-remaining header is skipped (stays null), not recorded as 0", async () => {
+    const headers = { "x-ratelimit-remaining": "   " };
+    vi.stubGlobal("fetch", async (input: RequestInfo | URL) => {
+      const url = String(input);
+      if (url.endsWith("/contents/AI-USAGE.md")) return Response.json({}, { status: 404, headers });
+      if (url.endsWith("/contents/CONTRIBUTING.md"))
+        return Response.json({ type: "file", encoding: "base64", content: Buffer.from("Contributions welcome.", "utf8").toString("base64") }, { headers });
+      if (url.includes("/issues?")) return Response.json([issue(3)], { headers });
+      return Response.json({}, { status: 404, headers });
+    });
+
+    const result = await fetchCandidateIssuesWithSummary([{ owner: "acme", repo: "widgets" }], "token", { apiBaseUrl: API });
+
+    expect(result.rateLimitRemaining).toBeNull();
+  });
+
+  it("#9678: a genuinely-present '0' x-ratelimit-remaining is still recorded (real exhaustion is not lost)", async () => {
+    const headers = { "x-ratelimit-remaining": "0" };
+    vi.stubGlobal("fetch", async (input: RequestInfo | URL) => {
+      const url = String(input);
+      if (url.endsWith("/contents/AI-USAGE.md")) return Response.json({}, { status: 404, headers });
+      if (url.endsWith("/contents/CONTRIBUTING.md"))
+        return Response.json({ type: "file", encoding: "base64", content: Buffer.from("Contributions welcome.", "utf8").toString("base64") }, { headers });
+      if (url.includes("/issues?")) return Response.json([issue(3)], { headers });
+      return Response.json({}, { status: 404, headers });
+    });
+
+    const result = await fetchCandidateIssuesWithSummary([{ owner: "acme", repo: "widgets" }], "token", { apiBaseUrl: API });
+
+    expect(result.rateLimitRemaining).toBe(0);
+  });
+
   it("treats a malformed (array, not object) policy-doc payload as absent content, and passes through non-base64-encoded content unchanged", async () => {
     vi.stubGlobal("fetch", async (input: RequestInfo | URL) => {
       const url = String(input);